Which of these graphs represents a function?

A graph plots an ellipse through the points (negative 5, 3), (negative 5, 2), (0, 1), (1, 1), (2, 1), (5, 3), (2, 4), (0 4) and (negative 2, 4) on the x y coordinate plane.
W. A parabola declines through (negative 5, 2), (negative 3, 0), (negative 2, 0), (0, 1), (1, 2), (2, 3), (3, 5) on the x y coordinate plane.
X.
A curve declines from (0, 6) through (2, 5), (3, 3), (3, 2), (3, 1), (2 points 5, negative 3), (2 points 3, negative 4) and (2 points 2, negative 5) on the x y coordinate plane.
Y. A curve declines from (5, 5), (3, 5), (2, 4 points 9), (negative 1, 4), (negative 2, 4), (negative 3, 3), (negative 2, 2), (0, 1 point 5), (2, 1), (3, 10, (4, 1) and (5, 1) on the x y coordinate plane.
Z.